Business, science and entertainment applications depend upon computers to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 512 or more data tracks.
The improvement in magnetic medium data storage capacity arises in large part from improvements in the magnetic head assembly used for reading and writing data on the magnetic storage medium. In operation the magnetic storage medium, such as a tape or a magnetic disk surface, is passed over the magnetic read/write (R/W) head assembly for reading data therefrom and writing data thereto.
As capacity increases, it is desirable to also increase the system's performance which includes the data rate during writing operations. One limitation to this data rate is the current rise time in the inductive coil of the writer. Several factors limit this current rise time. One factor of particular interest is the retardation of the rise time due to impedance mismatching between the output impedance of the write driver and the characteristic impedance of the cable. Such impedance mismatching results in reflections which lead to slower current rise times.
What is therefore needed is a way to improve the matching between write signal generator circuit and the characteristic impedance of the cable used to deliver power to the write head.
One solution to the problem is to change the output impedance of the write drive to match the characteristic impedance of the cable. However, in a voltage type driver, the output resistance is dominated by a series resistance which is chosen to set the steady state current required for optimally written magnetic patterns on the tape. Since the write current is generally determined by the write head design, there is not much freedom in the design to change the value of this series resistance.
A second possible solution is to adjust the cable conductor width and spacing and insulator dielectric constant to produce a cable with a characteristic impedance which matches the series resistance. However, cable fabrication technology and restrictions on the cable flexibility limit the range of impedances that can be achieved with the cable.
A third solution is to move the write signal generator proximate to the head, thus effectively removing the cable impedance from the write signal generator circuit. However, this has the disadvantage that logic signal lines must be added to the cable, making the cabling more complex and stiff. Further, the write driver becomes more complex and there may not be enough space for locating the driver chip proximate to the head.